The invention relates to a collecting device for collecting floating dusts in the atmosphere; a method for measuring a particle size distribution of the floating dusts collected by the collecting device; and a method for measuring a quantity, shape and component of the floating dusts in the atmosphere.
Among the fine particles floating in the atmosphere, those particles having a diameter less than 10 μm are called suspended particle matter (SPM). Although these floating dusts contain sands, they are mainly composed of black smokes, unburned materials, sulfur compounds and the like (35% of these is generated from diesel engine cars in the Kanto District, Japan), and it is said that they are highly toxic. The dusts from the exhaust gas from the diesel engine car are specially called diesel exhaust particles (DEP). Also, the particles floating in the atmosphere having a particle smaller than 2.5 μm are called micro-particulate matter (PM 2.5), and have been extensively researched and studied. It is said that the exhaust gas from the diesel engine car is a likely source of the PM 2.5.
In addition, as the particulate matters floating in the atmosphere, the yellow sands can be mentioned. The yellow sands are blown up by strong wind at inland desert of Chinese Continent and carried to Japan over the sea by the strong westerlies. Although particle diameters of the yellow sands differ depending on a location, the yellow sands in Chinese Continent near the desert have particle diameters in a range of 20 to 30 μm, and the particles reaching Japan far from the desert have diameters in the order of 4 to 5 μm.
Further, the particulate matters floating in the atmosphere include pollens. Recently, with increase in the number of people who suffered from a variety of pollinosis, information on the pollens floating in the atmosphere becomes important. The pollens of Japanese cedars and Japanese cypresses are said to be main causes of the pollinosis. The pollens of these plants have substantially a sphere shape with a diameter in the order of 30 to 50 μm.
As a method for measuring the floating dusts described above, there has been a method wherein the atmosphere is sucked in and passed through a filter to collect the floating dusts on the filter. Then, a microscope is used to observe the dusts for determining shapes and the number of the particles. There has been also a method wherein the floating dusts in a certain volume of the atmosphere are collected on the filter in the above-stated method, and weights of the filter before and after the collection are measured to obtain the quantity of the particles. In addition, there has been a method wherein the floating dusts collected on the filter in the same manner as described above are processed, and the extracted chemical components contained in the floating dusts are identified by a gas chromatograph mass spectrometer, liquid chromatograph mass spectrometer or spectrum analyzer.
Also, to measure a particle size distribution of the floating dusts (SPM) and micro-particulate matters (PM 2.5) in the atmosphere described above, a cascade-impactor type device has been practically used. The cascade-impactor type device utilizes an impacting process of suddenly changing a flow direction of a medium with the particles through colliding against a collecting plate, thereby separating the particles with a specific size from the medium. The cascade-impactor type device is structured such that a plurality of impactors, each having a 50% collecting efficiency at a specific particle diameter, is connected in series of multi-stage. A particle diameter of the dusts collected with the 50% efficiency at each stage represents an average particle diameter for each stage. Thus, the particle size distribution can be obtained from the quantity of the dusts collected from each stage.
Also, as a collecting method of the pollens floating in the atmosphere, a slide glass with an adhesive such as Vaseline coated on a surface has been used. The slide glass with the adhesive thereon is placed in the atmosphere, thereby allowing the pollens in the atmosphere to fall down thereon. The pollens adhered to the slide glass are observed by the microscope to thereby measure a shape, size, number, kind and the like.
Also, as a method for measuring a concentration of the floating dusts, there has been used a method wherein a certain volume of the atmosphere is sucked in and passed through a filter to trap the dusts therein. Then, weights of the filter before and after the collection are measured with an electronic balance or the like. The concentration of the floating dusts in the certain volume of the atmosphere can be determined from the weight difference.
Also, as a device for effectively collecting the floating dusts in the atmosphere, an electrostatic-type particle collector has been known. In the electrostatic-type device, the particles floating in the atmosphere are charged by ions generated from a discharge electrode. A dust-collecting electrode with a different potential relative to the discharge electrode is disposed to collect the charged particles. As the discharge electrode, a discharge electrode as shown in FIG. 14 has been often used in the electrostatic-type particle collector. The discharge electrode is formed of a number, i.e. several hundreds, of metal wires, and the wires are bundled with a brush tip at one end.
In the collecting method using the filter to analyze SPM and PM 2.5 with the microscope or various chemical analyzing instruments, it is very difficult to extract the floating dusts individually. Therefore, in the case of the microscopic observation, the floating dusts adhered to the filter are observed with the microscope as they are. In this case, the particle image may be blurred because of a background filter image. Also, in the case of conducting various chemical analyses, since the floating dusts are difficult to remove from the filter, it is difficult to do the analyses. For example, in the case of a fluorescent X-ray analyzer, it is difficult to irradiate the X-ray only on the particles.
Further, it is difficult to conduct the spectrum analysis, since the floating dusts are not separated each other on the filter and electromagnetic wave is difficult to focus on a single particle. Also, the gas chromatograph mass spectrometer or the like is difficult to apply as the floating dusts are hardly separated from the filter.
In the conventional method for measuring the concentration of the floating dusts, the filter is easy to absorb water, thereby causing an error in measuring the floating dusts due to the absorbed water. Also, in this method, it is necessary to weigh the filter twice. Therefore, it is difficult to measure a real time change in the concentration, and the work is also troublesome.
Moreover, in the case that a laser diffraction particle size analyzer is used to determine the particle size distribution, it is necessary to irradiate a laser beam to the floating dusts having a concentration within a specific range to obtain appropriate diffracted or scattered light. In order to provide the floating dusts in the concentration range suitable for the measurement, for example, a specific quantity of the floating dusts may be collected through suction of the atmosphere for a certain period of time. However, the concentration of the floating dusts in the atmosphere is not constant and varies even during the collecting operation. Thus, at the time point when the collecting is completed, the quantity of the floating dusts is totally different from an expected value, and it is difficult to obtain a sample at a desired concentration.
Also, it takes long time to collect the pollens on the surface of the slide glass, for example, 24 hours, in the conventional method for collecting the pollens floating in the atmosphere. Also, a collected quantity per a specific period of time is influenced by wind and the like, so the collected quantity does not represent the actual pollen quantity existing in the atmosphere.
Also, when the microscope is used to observe the collected pollens, it is relatively easy to identify the shape and kind of the pollens. However, the information does not represent the whole pollens floating in the atmosphere since the. collected pollens are influenced by wind and the like. Further, it is necessary to measure the respective diameters of the pollens to obtain a particle size distribution of the pollens, resulting in a complicated work.
In the conventional measuring device based on the cascade impactor method for measuring the particle size distribution of the floating dusts, an upper limit of the measurement is theoretically in the order of 10 μm. In addition, the number of the collecting plates determines a resolution of the measurement. Therefore, even though it is desired that the particle size distribution be measured at a high resolution, there is a limitation.
In the conventional electrostatic-type particle collector as described above, it takes long time to manufacture the discharge electrode since a large number of metal wires need to be bundled together. In addition, it is necessary to have a step of making one end thereof in a brush shape, resulting in a high cost. Further, in addition to the cost, it is difficult to make the shape and structure of the discharge electrode uniform, resulting in a large variation in efficiency of generating the ions and collecting the particles in the particle collector.
In view of the above defects, the present invention has been made and an object of the present invention is to provide a device for collecting the floating dusts in the atmosphere, wherein the collected particles can be easily observed by the microscope and individual particles can be easily extracted for various analysis techniques. Another object of the invention is to provide a method for easily measuring the particle size distribution of the floating dusts in a wide range including particle diameter larger than 10 μm with a high resolution.
In addition, an object of the invention is to provide a method for clearly observing the floating dusts in the atmosphere by the microscope without influence of the background.
Also, another object of the invention is to provide a method for accurately measuring the quantity of the floating dusts in the atmosphere.
Further object of the invention is to provide a method for accurately identifying the chemical components contained in the floating dusts when analyzed by the gas chromatograph mass spectrometer and the spectrophotometer.
Further, an object of the invention is to provide a device for measuring a concentration of the dusts, wherein a real time change in concentration of the floating dusts in the atmosphere can be measured with a simple operation, and the collected floating dusts can be easily subjected to various measurements. Also, an object is to provide a collecting device for securely collecting the floating dusts in a specific concentration range.
Further, an object of the invention is to provide a collecting method wherein the yellow dusts in the atmosphere are effectively collected, and the collected dusts are easily subjected to the microscopic observation and various analyses. Another object of the invention is to provide a measuring method for measuring the particle size distribution and the concentration of the collected dusts at a high resolution.
In addition, an object of the invention is to provide a collecting device for securely collecting the pollens floating in the atmosphere without influence of the wind or the like. Another object of the invention is to provide a measuring device for easily and accurately measuring the particle size distribution of the pollens floating in the atmosphere as well as the shape, kind and number of the pollens floating in the atmosphere without influence of the wind or the like.
In the conventional electrostatic type particle collector, the discharge electrode is formed of a large number of metal wires, and one end of thereof is formed in a shape of the brush tip. An object of the invention is to provide an electrostatic type particle collector having a particle collecting efficiency equal to or better than that of the conventional device with a new type of electrode. The present invention can reduce a manufacturing cost and have good reproducibility, thereby improving the quality of the products.
The present invention is to provide a particle collector, wherein the dusts floating in the atmosphere can be collected effectively. The collected dusts can be easily preserved as they are. As a result, it is easy to observe the collected dusts with the microscope. In addition, the collected dusts can be individually extracted, thereby easily applying the various analyses including the laser diffraction-scattering type particle size distribution device.
Further objects and advantages of the invention will be apparent from the following description of the invention.